Spark plug



l Aug. 29, 1939. Hf RABEzzANA SPARK PLUG Filed Junel 6, 1938 n' NRW@ X.

3 n n en tor eczaz @Mezzana Patented Aug. 29, 1939 UNITED STATES PATENT oFFicE 2,171,164 SPARK PLUG Hector Rabezzana., Flint, Michs'assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application June 6, y1938, `Serial No. 211,998

Claims.

shell, and electrodes one carried by said insulating member and the other by said shell, said insulating member being permanently held in place within said shell which, in addition to housing said member, serves as a support for suitable 0 means for connecting a supply conductor to the plug so as to supply current thereto; and the objects of my invention are to provide a. spark plug having the features enumerated and wherein a more perfect gas tight joint is secured between the insulating member and the shell than has heretofore been the case, to provide an improved grounded or shell electrode, and to provide such other improvements in spark plugs as are hereinafter described.

In the preferred form of my invention illustrated and described the connecting means includes a. metallic tube to which a braided wire covering or equivalent metallic shield upon the supply conductor may be connected, whereby a shielded system isprovided to prevent the high tension current supplied to the plug from interferring` with adjacent radio receiving apparatus; which is of great importance when the plugs are used in engines used to propel airplanes. The shell, the insulator, the electrodes and the means for holding the insulator permanently assembled within the shell, however, provide a, spark plug assembly which is complete in itself and capable of Vuse with connecting means other than the particular means illustrated, which in addition to its connecting function provides radio shielding for the supply conductor. Y

The drawing accompanying and forming a part of this specification illustrates the preferred form of my invention, although the same may be embodied in other specific forms and my invention is regarded as including such modications and variations of the particular form illus-- trated and hereinafter described as come within the scope of the concluding claims.

In the drawing:

Figure 1 is a. view showing a section of my proved spark plug in connection with supply conductor connecting means which provides radio shielding for the purpose stated.

Figure 2` is a view showing a section' upon a transverse plane indicated by the line 2 2, Figure 1.

Figure 3 is a view showing the lower end of the plug from a position beneath the same, looking up.

Figure 4 isa view showing my improved spark plug used with supply Vconductor connecting means different from the form shown in Figure 1.

Referring now to the drawing, the numeral 6 designates a hollow spark plug shell or casing made, ordinarily, from bar steel stock, and

the lower end of which is externally threaded 10 to screw into a threaded opening in an internal combustion engine cylinder. This shell has an internal ledge I which Supports the insulating member of the plug to which end said member is provided with a lower shoulder 8 disposed above said ledge, a packing gasket 9 being commonly interposed between the shoulder and ledges as shown. The insulating member shown is made of porcelain or equivalent ceramic material having the heat resisting and other properties requisite in spark plugs; and the central insulated electrode I0 of the plug extends through a passage therein and terminates within an opening in the grounded or shell electrode of the plug. The upper end of the electrode I0 is shown as connected to a metallic washer II which rests upon the upper end of the insulating member, the extremity of the electrode extending through a hole in the washer and being riveted'over or staked in place to fasten the parts together. The upper end of the insulating member extends above 0r beyond the upper end of the shell as shown.

'I'he upper end I2 of the shell 6 is shown as hexagonal in form to receive a suitable wrench, and this upper end is internally threaded as at I3; and the insulating member includes a central portion I4 the diameter 0f which is slight- 1y less than the internal diameter of the shell 6 whereby an upper shoulder I5 is provided. The end parts of the insulator below and above the shoulders 1 and I5 are of lesser diameter than the enlarged central portion `thereof as shown.

Surrounding the insulating member and contacting with the upper shoulder I5 thereofl is an annular holding member I6 which is C-shaped in cross section, and is made of spring steel or equivalent material; whereby a slightly yieldable member in the general form of a gasket is provided which, because` of its C-shaped form, is extremely stiff and serves to maintain -gas tightness between the lower shoulder 8, the gasket 9 and the supporting ledge l in the completed plug. That is, while in the completed plug the member I6 is forced into firm engagement with the upper shoulder l5, leakage of gas through the shell is prevented mainly if not wholly by the gasket 9 at the lower end of the insulating member.

' The c-shaped member i6 is held in place by an annular sleeve il the exterior of which is threaded and engages the internal threaded part I2 of the upper end of the shell, and the lower end of which fits within an annular recess I8 formed in the shell or casing 5 and engages the upper end of said member as shown. 'Ihis sleeve is shorter than the internally threaded upper end of the shell so that said upper end extends above the upper end of the sleeve, and the interior of said sleeve is shown as tapered so that it may be screwed into firm contact with upper end of the member i6 by a driver having a. correspondingly shaped end, to thereby force said member into iirm engagement with the shoulder l5. This method of assembly stresses the holding member IG and results in that the lower shoulder 8 is held in engagement with the gasket 9 by the resilient action of said holding member in the completed plug.

In assembling the parts thus far enumerated the insulating member is placed upon the lower gasket 9, the C-shaped holding member I6 is put in place, and the sleeve I1 is screwed into firm contact with the upper end of the member I6 with sufcient force to stress or load said member, whereby the insulating member is forced against the lower gasket 9 by the resilient action of said holding member. This holds the parts in permanently assembledrelation to one another and provides a plug which will ordinarily be sufciently gas tight when used in engines wherein the pressure within the engine cylinder is not excessive.

In order, however, to secure more perfect gas tightness when the plug is used under such high temperature and high pressure conditions as are met with in airplane service the upper end of the shell or casing is provided with a circumferentially extending groove whereby the wall thereof is reduced in thickness, as shown at i9; and, after the parts have been assembled as above explained, said thin wall section is collapsed slightly, thereby securing increased tightness at the lower gasket 9.' This collapsing of the thin wall section is preferably accomplished by heating said sectionV by a current of electricity caused to ilow therethrough by contacts of a suitable electric welding or riveting device which engage the upper and lower parts of the plug. Then and while the wall section i9 is plastic, due to the heating thereof, pressure (by and through the contacts) is applied thereto, whereby more perfect joints are secured between the C-shaped member I6 and the upper shoulder l5, and between the lower shoulder 8 and gasket 9 and the ledge l. The pressure is maintained vuntil the thin wall section becomes cool and said section as it contracts acts further to produce gas tightv joints between the shell or casing and the insulating member of the plug.

The spark plug herein described is especially adapted to be used with other elements to provide ashielded spark plug, designed for use in airplane engines to prevent the high tension current supplied to the plugs from interferring with the operation of adjacent radio receiving apparatus; and my invention regarded in its more specific aspect includes a metallic shield tube 2B made, preferably, of stainless steel, and the lower end 2l of which is threaded and screws intq the upper end of the internally threaded part l2 of the shell of the plug. This shield tube has a lining 22 of insulating material such, for example, as Bakelite, and the same may be moulded inside the tube so as to be in effect integral therewith,

or it may be formed as an element separable from the tube and of such shape as to t closely therein. Whichever way it is formed the lower end 23 thereof extends beyond the lower end of the shield tube 20 and into the annular sleeve il as shown.

Current is supplied to the central electrode l@ through a supply cable having a conductor 203, and an insulating covering of rubber or equivalent material 2'3. 'I'he cable has an external metallic sheath such as braided wire covering, al flexible metal tube; or equivalent device; and this sheath iselectrieally connected to the shield tube 20 by a suitable coupling which engages a threaded portion 25 at the upper end thereof. The end of the cable inside the lining 22 is shown as surrounded by a sleeve 26 of insulating material such as Bakelite, andan electrical connection between the conducting wire 23 and the washer Il and central electrode Hl is provided by a metallic spring 2. These parts for connecting the supply cable to the central electrode of the plug, and for connecting a sheath thereof to the shield tube 20 to accomplish grounding of the shield to the shell 6 of the plug, however, form no part of the invention to which this present application relates, and the showing of these parts is a conventional showing to explain the relation of the plug parts to other elements of the ignition system of an engine.

It will be appreciated that the shell or casing the insulating member within the same, the

annular sleeve Il and the C-shaped member IE whereby the insulating member is permanently held in assembled relation to the shell, together with the electrodes, provided a unitary spark plug assembly separate from the means (the shieldY tube 2D in the device herein described) carried by the shell for connecting the supply conductor to the plug; and that the shield tube 2B while it is claimed in some of the claims in combination with spark plug features is an element separate from the plug per se, and is in effect a part of the usual harness whereby a current supply conductor is connected to the plug so as to supply current to the insulated electrode thereof. The plug itself is therefore an assemblage separate from the shield tube, the insulating lining 22 therefor and other parts of the ignition harness proper, and may be used with other means carried by the shell for connecting the supply conductor to the central electrode, but which other connecting means do not provide radio shielding for supply conductor.

The grounded or shell electrode 2l is in the form of a transverse bar both ends ef which are welded to. the inner extremity of the shell thereby providing large areas of contact between the electrode and the shell. This electrode has -a central circular opening 28 into which the lower end of the central electrode ill extends, and slots 29, 30 extend from said opening outwardly and toward the periphery of the shell. of these features is to provide for convenient adjustment of the spark gap as it will be appreciated that if the gap becomes too long, due to wear of the end o f the central electrode and the wall of the opening into which it extends, the length thereof may be reduced by forcing the sides The purpose provided by the central opening and slots toward 75 with connecting means carried by the shell or casing for connecting a supply conductor to the plug, but in which radio shielding is not present. In said figure the shell, the insulating member, and the means for holding said member permanently assembledwithin the shell are the same as shown in Figure 1 and hereinbefore described; but in this figure the cap 3| which encloses the upper end of the insulating member, and which screws into-the upper internally threaded part l I2 of the shell, is made of an insulating material such as Bakelite and carries a terminal post 32 to which a supply conductor may be connected by a suitable connector, a conducting path to the central electrode being provided by a spring 33 corresponding with the spring 21 in the form of my invention illustrated in Figure 1.

Having thus described and explained my invention I claim and desire to secure by Letters Patent:

l. In a spark plug of the class described, a hollow metallic shell or casing which is externally threaded to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded; an insulating member within said shell and having upper and lower shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is supported; an externally threaded annular sleeve within the upper internally threaded part of said shell; an annular holding member located between the lower end of said sleeve and the upper shoulder of said insulating member; a tubular metallic shield the lower end of which is threaded and screws into the threaded upper end of said shell; and a lining of insulating material within said shield and surrounding the upper end of said insulating member.

2. In a spark plug of the class described, a hollow metallic shell or casing which is externally threaded to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded; an insulating member within said shell and having upper and lower shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said`shell whereby said insulating member is supported an externally threaded annular sleeve within the upper internally threaded part of said shell; a resilient annular metallic holding member C- shaped in cross section located between the lower end of said annular sleeve and the upper shoulder of said insulating member; a tubular metallic shield the lower end of which isthreaded and screws into the threaded upper end of said shell; and a lining of insulating material within said shield and surrounding the upper end of said insulating member, and the lower end of which lining extends beyond said shield and into said annular sleeve.

3. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded and has an external circumferentially extending groove, and an internal annular recess; an insulating member within said shell and having lower'and upper shoulders spaced apart from one another, and the`upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is supported; an externally threaded annular sleeve Within the upper internally threaded part of said f shell, and the lower end of which extends into the annular recess aforesaid; and an annular holding member located between the lower end of said sleeve and the upper shoulder of said insulating member.

4. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded and hasan external circumferentially extending groove, and an internal annular recess; an insulating member within said shell and having lower and upper shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is supported; an externally threaded annular sleeve within the upper internally threaded part of said shell, and the lower end of which extends into the annular recess aforesaid; and a resilient annular metallic holding member C-shaped in cross section located between the lower end of said annular sleeve and the upper shoulder of said insulating member.

5. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, andthe upper end of which is internally threaded and has an external circumferentially extending groove, and an internal annular recess; an insulating member within said shell and having lower and upper shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge Within said shell whereby said insulating member is supported; an externally threaded annular sleeve within the upper internally threaded part of said shell, and the lower end of which extends into the annular recess aforesaid; a resilient annular metallic holding member C-shaped in cross section located between the lower end of said annular sleeve and the upper shoulder of said insulating member; a tubular metallic shield the lower end of which is threaded and screws into the threaded upper end of sai-d shell; land a lining of insulating material within said shell and surrounding the upper end of said insulating member.

6. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded and has an external circumferentially extending groove, and an internal annular recess; an insulating member within said shell and having lower and upper shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is supported; an externally threaded annular sleeve within the upper internally threaded part of said shell, and the lower end of which extends into the annular recess aforesaid; a resilient annular metallic holding member C-shaped in cross section located between the lower end of said annular sleeve and the upper shoulder of said insulating member; and a metallic shield the lower end of which is threaded and screws into the threaded upper end of said shell.

7. In a spark plug of the class described, a hollow metallic shell or casing having an eX- ternally threaded part at itsvlower end to screw into a threaded opening in an engine cylinder; and the upper end of which is internally threaded and has an external circumferentially extending groove whereby a shell wall thickness of reduced area is provided at the bottom of said groove, and which shell has an internal annular recess below said groove; an insulating member within said shell and having lower and upper shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is supported; an externally threaded annular sleeve within and of less length than the upper internally threaded part of said shell, and the lower end of which extends into the annular recess aforesaid; and an annular'holding member located between the lower end of said sleeve and the upper shoulder of said insulating member; the wall section of reduced area at the bottom of said groove having been collapsed after the insulating member has been assembled within the shell and after said annular holding member has been screwed into the upper threaded part of 4said casing to hold said insulator in place therein.

8. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded and has an external circumferentially extending groove whereby a shell wall thickness of reduced area is provided at the bottom of said groove; an insulating member within said shell and having lower and upper shoulders spaced` apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is supported; an externally threaded annular sleeve within and of less length than the upper internally threaded part of said shell; and an annular holding member located between the lower end of said sleeve and the upper shoul- ,der of said insulating member; the wall section of reduced area at the bottom of said groove having been collapsed after the insulating member has been assembled within the shell and after said annular holding member has been screwed into the 4upper threaded part of said casing to hold 4said insulator in place therein.

9. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, and the upper end of which is internallythreaded and has an external circumferentially extending groove whereby a shell wall thickness of reduced area. Iis provided at the bottom of said groove, and which shell has an internal annular recess below said groove; an insulating member within said shell and having lower and upper shoulders spaced apart from one another, and the upper end `of which insulating member extends above said shell; a ledge within said shell whereby said insulating member ls supported; an externally threaded annular sleeve within and of less length than the upper internally threaded part of said shell; and the lower end of which extends into the annular recess aforesaid; and a resilient annular metallic holding member C-shaped in cross-section located between the lower end of said sleeve and the upper shoulder of said insulating member; the wall section of reduced area at the bottom of said groove having been collapsed after the insulating member has been assembled within the shell and after said annular holding member has been screwed into the upper threaded part of said casing to hold said insulator in place therein.

10. In a spark plug of the class described, a hollow metallic shell or casing having an externally threaded part at its lower end to screw into a threaded opening in an engine cylinder, and the upper end of which is internally threaded and has an external circumferentially extending groove whereby a shell wall thickness of reduced area is provided at the bottom of said groove; an insulating member within said shell and having lower and upper shoulders spaced apart from one another, and the upper end of which insulating member extends above said shell; a ledge within said shell whereby said insulating member is lsupported; an externally threaded annular sleeve within and of less length than -the lupper internally threaded part of said shell; and a resilient annular metallic holding member C-shaped in cross-section located between the lower end of said sleeve and the upper shoulder of said insulating member; the wall section of reduced area at the bottom of said groove havingbeen collapsed after the insulating member has been assembled within the shell and after said annular holding member has been screwed into the upper threaded part of said casing to hold said insulator in place therein.

HECTOR RABEZZANA. 

